What is the size of the Section vector of certain data type in wasm binary?

Question

I am reading this docs. I have doubt about the content of the vector of the sections in binary. For eg Table Section here. How many items of type tabletype can be present in that vector<tabletype>. Is it 0,1 and more or 0(not present) and 1 (only one present)?

Answer 1

The table section is made of vector of tables: vec(table). Each table has one tabletype. From here:

Vectors are encoded with their u32 length followed 
by the encoding of their element sequence.

This means that a module might have [0..2^32) tables, each with its owntabletype. That said, it is expected, that some "reasonable" limitation is placed on the number of tables (and other objects) that a program is willing to load.

If there are no tables, the section might be omitted:

Every section is optional; an omitted section is equivalent 
to the section being present with empty contents.

This makes a total of three ways to have no tables: no section; empty section; section with a zero length tables vector.

As usual, when de-serializing (parse) one might expect all cases, but the when serializing (generate) it is better to have the minimum number of bytes.